ac3enc: Add x86-optimized function to speed up log2_tab().

AC3DSPContext.ac3_max_msb_abs_int16() finds the maximum MSB of the absolute
value of each element in an array of int16_t.

Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit fbb6b49dabc3398440c6dfa838aa090a7a6ebc0d)

1 files changed, 3 insertions, 8 deletions

diff --git a/libavcodec/ac3enc_fixed.c b/libavcodec/ac3enc_fixed.c
index 0db41dff2d..3de00ee484 100644
--- a/libavcodec/ac3enc_fixed.c
+++ b/libavcodec/ac3enc_fixed.c
@@ -270,14 +270,9 @@ static void apply_window(DSPContext *dsp, int16_t *output, const int16_t *input,
  * @param n   number of values in the array
  * @return    log2(max(abs(tab[])))
  */
-static int log2_tab(int16_t *tab, int n)
+static int log2_tab(AC3EncodeContext *s, int16_t *src, int len)
 {
-    int i, v;
-
-    v = 0;
-    for (i = 0; i < n; i++)
-        v |= abs(tab[i]);
-
+    int v = s->ac3dsp.ac3_max_msb_abs_int16(src, len);
     return av_log2(v);
 }
 
@@ -308,7 +303,7 @@ static void lshift_tab(int16_t *tab, int n, unsigned int lshift)
  */
 static int normalize_samples(AC3EncodeContext *s)
 {
-    int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
+    int v = 14 - log2_tab(s, s->windowed_samples, AC3_WINDOW_SIZE);
     lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
     return v - 9;
 }